The present invention relates to a method for shaping panels, in particular aircraft fuselage skin sections, by means of bending. Such panels consist of a material which is elastically and plastically deformable, and in case of aircraft fuselage skin sections, is preferably of aluminum.
Aircraft, whether military or civil, must meet extreme requirements. Nevertheless, their manufacture should not involve excessive cost. These somewhat contradictory criteria apply in particular to the manufacture of curved skin sections or panels used for the fuselage, the wings, and other parts of aircraft.
Recent developments in the design of aircraft has resulting in panels or skin sections having an outer skin portion and reinforcing ribs or so-called "stringers" as integrally formed members. By means of modern milling machines, panels having at each point calculated minimum dimensions of skin, ribs and, as the case may be, additional fins intersecting the ribs, may be manufactured of solid aluminum sheet material.
Considerable problems, however, exist in the shaping of such integral panels to a curvature provided in accordance with a given pattern; the combination of skin, ribs, and fins intersecting the ribs, renders these panels very stiff and resistant to deformation.
Several methods are known by which such panels may be shaped: Stretch-drawing, ball blasting, rolling, and whipping. However, these processes involve difficulties when applied to integral panels.
Stretch-drawing results in locally inappropriate deformations unless very expensive apparatus is provided. Ball blasting is suitable only if the skin thickness exceeds a predetermined minimum to allow for the necessary skin dilation. Rolling and whipping are subject to limitations as to the shapes which may be obtained; in particular, there are problems with non-cylindrical or spherically curved workpieces, and this is particularly true when the ribs and fins of the panel have different height dimensions.